This invention concerns ionization chamber x-ray detectors. More specifically, this invention concerns improved one-dimensional arrays of parallel plate ionization chambers.
U.S. patent application, Ser. No. 544,171 (now abandoned) and Ser. No. 616,930 by John M. Houston and Nathan R. Whetten, which are assigned to the assignee of this invention, describe arrays of ionization chamber type x-ray detectors which incorporate high pressure xenon gas. A preferred embodiment of those detectors comprises a linear array of parallel plate electrodes defining a series of spatially distinct detection cells. Alternate electrode plates in the array are connected to electronic current sensors to produce signals which may be utilized to calculate a spatial distribution of x-ray intensity. Detectors of this type, by way of example, are particularly suited for use in computerized x-ray axial tomography systems.
The parallel plate electrodes of the above-described detector array operate in close proximity at relatively large potential difference. Mechanical vibration transmitted to the plates may, therefore, significantly vary the capacitance between electrodes and thus introduce microphonic current changes which are detected in the current sensing electronics and may introduce errors into an x-ray measurement. Glass or ceramic insulators, which are commonly used for mounting electrodes in ionization chambers, tend to transmit such mechanical vibrations to the detector electrodes.
Plastic resins and composite materials have been used to support and insulate electrodes in ionization chambers. Many dielectrics of the prior art exhibit relatively high photoconductive effects in the presence of x-ray electromagnetic energy. These photoconductive currents combine with the ionization current in the xenon gas to produce errors in the output signals of the above-described detector array.